Our alum Ian Sun developed this simple H-drive suspension system for the 2015 season. It was implemented in our Recycle Rush robot, and is fairly easy to reproduce.
Two 3D-printed brackets suspend, and allow to freely rotate, the CIM driving the center (strafing) wheel. Springs attached between the center wheel gearbox (in this case an AM Toughbox Nano) and the chassis provide passive suspension, maintaining constant contact with the ground.
Download it here. This model provides the AM14U chassis as an example implementation for the suspension system, springs aren’t included.
A photo of our implementation is available here, just imagine the center traction wheel is an omni-wheel.